Isocyanate reactive mixtures often contain polyols that are the polymerization products of alkylene oxides with polyhydric alcohols. In the preparation of such polyoxyalkylene polyols, starter compounds having active hydrogen atoms are oxyalkylated with alkylene oxides in the presence of a suitable catalyst. For many years, basic as well as double metal cyanide (DMC) catalysts have been used in oxyalkylation reactions to prepare polyoxyalkylene polyols.
Base-catalyzed oxyalkylation involves oxyalkylating a low molecular weight starter compound, such as propylene glycol or glycerine, with an alkylene oxide, such as ethylene oxide or propylene oxide, in the presence of a basic catalyst, such as potassium hydroxide (KOH) to form a polyoxyalkylene polyol.
One drawback to base-catalyzed oxyalkylation reactions is that propylene oxide and certain other alkylene oxides are subject to a competing internal rearrangement that generates unsaturated alcohols. For example, where KOH is used to catalyze an oxyalkylation reaction using propylene oxide, the resulting product will contain allyl alcohol-initiated, monofunctional impurities. As the molecular weight of the polyol increases, the isomerization reaction becomes more prevalent. As a result, 800 or higher equivalent weight poly(propylene oxide) products prepared with KOH tend to have significant quantities of monofunctional impurities that can reduce the average functionality and broaden the molecular weight distribution of the polyol.
Unlike basic catalysts, however, DMC catalysts do not significantly promote the isomerization of propylene oxide. Polyether, polyester and polyetherester polyols having low unsaturation values and relatively high molecular weights may be produced with DMC catalysts. Such polyols are useful in applications such as polyurethane coatings, elastomers, sealants, foams, adhesives and the like.
However, in some processes using isocyanate reactive mixtures that incorporate DMC-catalyzed polyols, brittle flakes have been observed forming in the manufacturing equipment. Those flakes have the potential of breaking off of the equipment and becoming integrated into the final product, resulting in a product having defects. Brittle flakes have heretofore not been observed in manufacturing equipment processing isocyanate reactive mixtures containing polyols prepared in the presence of a basic catalyst, such as KOH. One potential cause of this problem may be a difference in water compatibility between the polyols used in the mixture.
Therefore, a need exists in the art for an isocyanate reactive mixture having improved water compatibility to reduce or eliminate brittle flake formation in the manufacturing equipment and the resultant defects in finished products.